fix(docker): build context = pwap root so shared/ is reachable

Vite aliases @pezkuwi/utils → ../shared/utils, so the Docker build context
must include both web/ and shared/. Previous context: ./web missed shared/
which caused 'Could not load /shared/utils/formatting' at module resolution.

Changes:
- Dockerfile WORKDIR=/build/web; COPY web/* and shared/* explicitly
- Workflow context: ./ + file: ./web/Dockerfile
- Move .dockerignore from web/ to pwap root (matches new context)

.dockerignore

@@ -0,0 +1,41 @@
+# pwap/web Docker build context (root) — exclude everything not needed
+# for `web/` build. Other monorepo subprojects stay out of the image.
+
+# Other monorepo dirs (we only need web/ + shared/)
+exchange/
+mobile/
+pwap-mobile/
+docs/
+res/
+
+# All node_modules everywhere
+**/node_modules/
+**/dist/
+**/build/
+
+# Git, GitHub
+.git/
+.github/
+
+# Env files (built-in vars are passed as build-args from CI)
+**/.env
+**/.env.*
+!**/.env.example
+
+# Editor / OS
+.vscode/
+.idea/
+*.swp
+*.swo
+.DS_Store
+
+# Logs
+*.log
+
+# Cache
+**/.eslintcache
+**/coverage/
+
+# Already-built artifacts (we rebuild fresh inside container)
+web/dist/
+shared/**/dist/